PROJECT SUMMARY Cognitive deficits are a significant clinical problem associated with HIV infection (HIV-associated neurocognitive disorders or HAND). We have recently[1] showed that an HIV coat peptide (HIV Gp120 V3 loop peptide or HIV-V3 peptide), known to bind and activate a receptor that mediates HIV cellular entry (CCR5), caused acute memory deficits[1], that could be prevented by a CCR5 knockout or viral vector-mediated knockdown of this receptor[1]. Additionally, while transgenic overexpression of CCR5 in neurons resulted in hippocampus-dependent learning and memory deficits[1], decreasing the function of CCR5 enhances hippocampus-dependent memory (e.g., spatial and contextual learning) by enhancing canonical memory mechanisms, including MAPK/CREB signaling leading to enhanced long-term potentiation (LTP). Knock-down of this receptor in retrosplenial cortex (RSC) also enhances spatial learning, and two-photon microscopy studies of spine turnover in this structure showed that CCR5 knock out increases spine turnover before learning and spine clustering after learning, two structural markers of enhanced learning and memory. Overall, our results demonstrate that CCR5 plays an important role in neuroplasticity and learning and memory, and demonstrate that while knockdown of CCR5 enhances plasticity and learning, over-activation of this receptor has the opposite effect[1], suggesting that CCR5 over-activation by viral proteins may contribute to HAND[1] [2]. Here, we propose integrative multidisciplinary studies with state-of-the-art approaches, such as head- mounted fluorescent microscopes (miniscopes) developed in our laboratory that can be used to track neuronal activation in freely moving mice [3]. These studies have two key goals: 1- To determine whether the GFAP- gp120 transgenic model [2, 4] or the HIV-V3 peptide specifically targeted to the adult RSC, disrupt MAPK and CREB signaling, LTP, spatial and contextual learning and memory, and whether this can be prevented by a CCR5 knockout, viral knockdown of this receptor, or by a FDA approved drug that inhibits CCR5 (Maraviroc) with or without combination antiretroviral therapy (cART); 2- To test whether spatial representations, measured with GCAMP6f and miniscopes, in the hippocampus and in the RSC are disrupted by the HIV-V3 peptide or in the GFAP-gp120 transgenic model, and whether this can be prevented by a CCR5 knockout, CCR5 viral knockdown, or by cART with or without Maraviroc. Beyond elucidating molecular, cellular and circuit mechanisms responsible for the learning and memory deficits caused by HIV proteins, the studies proposed here will also test specific treatments that could be potentially used to design clinical interventions targeted to the earlier stages of HIV infection. The relative lack of neuropathology attributed to HIV infection in cART-treated subjects [5], argues that the mechanisms responsible for HAND are likely due to functional alterations in neurons, such as the ones we propose to study here.